We were halfway between Coney Island and John F. Kennedy International Airport when we saw the horses. There were six of them trooping along the sandy shoreline, which was a surprise to most of us on board The American Princess, but not to Dave Avrin of the National Parks Service. “You’ll see some folks riding horses in the middle of Brooklyn,” he said, as if we had seen a pizza place or a fire truck.

It was our fourth hour on the harbor tour of the inaugural Dredge Fest, and we were deep in Jamaica Bay, the body of water that separates Brooklyn and Queens from the Rockaways. We had been told many times not to expect visual thrills. "One of the challenges of giving a boat tour about dredging," Tim Maly, one of the event’s organizers, had said as we swung under the Verrazano Narrows Bridge, “is that an enormous part of the landscape is invisible, because it’s underwater, and we can’t see underwater."

"No refunds," he added.

Nevertheless, the boat had been swaying like a pendulum all afternoon as passengers crossed from gunwale to gunwale to see the tools and products of dredge. This was partly a matter of self-selection, since all of the 125 or so people on board had chosen to spend their Saturday afternoon touring the infrastructure of New York Harbor and learning about sediment control techniques.

But what we were witnessing was something more unusual: the final months of a 15-year transfer of dirt, enough to fill a football stadium the height of Mount Everest, from the bottom of New York Harbor to its shores, all for a design modification over 2,000 miles away and in another country.

This rather big idea had been introduced the previous day, while we were gathered in a Lower Manhattan loft for the ambitiously scheduled Dredge Fest symposium, which featured 13 experts and lasted from 1 p.m. till the sun went down. We learned about the Great Lakes, oysters, China, the Mississippi Delta, subway car reefs, the Rhine River, geotubes, containerization, and a great deal more about dredging, the mechanical movement of underwater sediments, the method by which humans have been reshaping our underwater environment for thousands of years.

The dredging going on in New York Harbor at the moment, whose fruits we saw in Jamaica Bay, is part of what the Dredge Fest team calls a "design shockwave." The Panama Canal is being expanded for the first time since its completion in 1914. The project, begun in 2006 and expected to finish in 2014, will allow larger ships to pass from the factories of East Asia to the ports of the East Coast.

The Panama Canal expansion has the potential to bring a significant amount of trade back to the U.S. East Coast from deep-water ports like Long Beach, California. Currently, the "Panamax" -- the maximum capacity of a ship that can fit through the canal -- is 5,000 T.E.U., or about 5,000 standard 20-foot shipping containers. After the renovations, it will be 13,000 T.E.U. Since 95 percent of the goods the U.S. imports come by ship, West Coast ports have long enjoyed a large advantage over their East Coast counterparts.

The expansion project has produced an explosion in the amount of dredging in this country, as the federal government spends billions in cities like Miami, Charleston, Savannah, Wilmington, and Jacksonville to deepen shipping channels. No one knows exactly the amount of dredging we do in this country. “Whatever it is,” said a former dredger at the symposium, “It’s about to change significantly. There’s a race from Brownsville to Boston to get deep. Everyone wants to get deep, not everyone can.” Hence the billion-dollar shockwave emanating from the Panamanian isthmus. Harbors from the Gulf Coast to Liverpool are being dredged for ships of a size that these cities have never seen before.

The Port of New York and New Jersey, experts say, will be ready. Since the Harbor Deepening Project began in the mid-1990s, the Army Corps of Engineers has scraped, sucked, drilled and bombed the bottom of the New York harbor from a depth of about 41 feet to a depth of 50 feet. By the time the it’s completed in early 2014, to coincide with the opening of the canal, the project will have dug up 30 Empire State Buildings worth of dredge material, from 35 miles of channel.

But that’s only half the game. What does a city do with 30 Empire State Buildings worth of sand and silt?

• • • • •

New York, the Dredge Fest team says, is a city built on dredge. Approaching the pier on Saturday afternoon, I see a sign on Pearl Street that validates this claim. There, four blocks from the water, lies the ragged 17th century shoreline of the East River. Landfill and dredge have fattened the island to its present shape. At one point, the city sold "water plots" of cheap, muddy, waterfront land near Pearl St. – the real estate equivalent of a fixer-upper. Now, this the heart of the Financial District.

On the upper level of The American Princess, docked at Pier 11, tour members assembled. We were a disparate bunch: historians, students, artists, photographers, dredgers, and a whole lot of architects. Many of us were bloggers. Nearly all had cameras, some of us had thermoses and bag lunches. We had been told to bring warm clothes.

Cameras at the ready for sediment pipes, freighters and other infrastructure sights.

The Dredge Fest team, Steven Becker, Brett Milligan, Rob Holmes and Tim Maly (on the weekdays, three architects and a journalist, respectively) have been looking at dredging together for about two years now, and their evident enthusiasm for all things dredge, broadcast through the P.A. system, kept the mood unfailingly upbeat. At one point, during the harbor tour, Becker will say: "I don't know if you got the same massive childlike excitement that I did when we first saw that floating piece of machinery in Ambrose Channel." At another, Maly will take the microphone and read from his phone an entire article from the Troy Record, an upstate New York newspaper: "Good Weather, Improved Techniques Accelerating Dredging Project.”

We sailed down through Upper New York Bay. Our southern trajectory had concentrated the Manhattan skyline beyond recognition. We were moving into a different kind of city, one whose foreignness robbed it of scale: towering cranes, dry docks, cylindrical oil tanks, bridges, swollen freighters with Cyrillic or Greek lettering across their backs. How tall is a freighter? Five stories? Twenty?

Cranes at Newark Bay, the largest port on the East Cost. Photo credit: Flickr user Dan Deluca.

Once, when the South Street Seaport was a seaport, New York was the shipping capital of the world. The city’s skyline was one of cedar masts and, later, steel hulls. One out of every six New Yorkers once had an income tied to the port. Even today, more than half the goods and people that have ever entered the United States have come through the New York harbor.

Though the salty sailors unloading crates on downtown docks are gone, replaced by the mechanical efficiency of container shipping in Newark Bay (the world’s first such facility opened at Elizabeth in 1962), the port is still a massive, regional industry, employing over a quarter of a million people. It is the third-largest port in the nation, and the largest for oil imports. But its geographic removal has made it nearly invisible to most New Yorkers. The tankers and freighters passing through the Verrazano Narrows turn up the Kill Van Kull and into Newark Bay, much closer to the Jersey Turnpike than to the Highline.

The Bayonne Bridge: a billion dollars short of a 65-foot lift. Photo credit: Flickr user saebaryo.

We cruised down the KVK towards the Bayonne Bridge. The Port Authority wants to raise the height of this 1931 steel arch bridgeby 65 feet when the harbor deepening project finishes in 2014. The bridge and its low air draft stand between the Newark shipping yards and the bay, literally in the way of the super-sized trade wave the Port Authority is expecting. “Big ships,” Becker remarks, “have to wait until the tide goes down to squeak under.” Raising the height of the bridge is expected to cost $1 billion.

Then we saw something that didn’t fit the scene at all: the Bayonne Golf Club, a patch of rolling hills topped by a clubhouse and an American flag. It is a new and acclaimed golf course – Sports Illustrated called it “the most audacious golf course in the world” – with membership available by invitation only. The views, evidently, are spectacular. It is also the largest placement site of dredge material in the harbor.

Broadly speaking, there are two kinds of material that the Army Corps dredges off the bottom of New York Harbor: sediment and sand. New York’s environmental laws have made sediment, usually contaminated by centuries of pollutants drifting down the Hudson, hard to get rid of once it has been brought off the harbor floor. Dirty silt currently ends up as far away as Pennsylvania. Dredging, treating, and shipping the stuff can cost $80 to $100 per cubic yard. That’s about ten times what it costs the Army Corps to get rid of clean dredged material, usually sand, which is finer and less likely to be corroded by chemicals. That can be dumped at the HARS, an ocean dumping site off Sandy Hook, New Jersey, for $8 to $10 dollars per cubic yard.

Watching islands take shape in Jamaica Bay.

It can also be put to "beneficial reuse," which has been the mission of Lisa Baron. Baron, an Army Corp of Engineers project manager and chief of the Harbor Programs Branch in 2011, was more or less conducting the tour. She's familiar with most of what you can see in the harbor and a lot that you can’t.

At Ambrose Channel, between Brooklyn and Staten Island, Baron says, the Army Corps had started digging up the “highest quality sand imaginable.” Kathy McGuckin, a fellow dredger along for the ride, says that it was so clean, “you could put it in a sandbox.” Or in a national park, which exactly is what the dredgers did.

The American Princess followed the journey of that sand, around Coney Island, under the Marine Parkway Gil Hodges Memorial Bridge, and into Jamaica Bay and the Gateway National Recreation Area. It was getting colder, but the crew was brewing coffee and the railings were still crowded with people. Avrin, who serves as chief of resources at Gateway, between pointing out kayakers, fishermen, and horses, notes that there are 350 species of birds in the park. Just beyond the marshes we can see the rising skeleton of One World Trade Center.

Jamaica Bay, like much of New York's harbor, was once a thriving wetland area. Pollution and erosion have since severely damaged its ecosystem. Though a large part of the bay was made part of Gateway in 1974, the first urban national park in the U.S., erosion continued. Acres of vibrant vegetated marsh habitat in the park dwindled from 2,347 in 1951 to 876 in 2003. Eighty percent of the islands had disappeared since 1924, and experts predicted they could all be gone by 2025.

Since then, the Army Corps has been barging sand into Jamaica Bay, where contractors use it to rebuild and regrow hundreds of acres of marsh islands, using a footprint of the bay’s land forms from 1974. “We are not going to see islands spring from Jamaica Bay,” Holmes had said, “We’re going to see sediment pipes.”

But on a geological time frame, these islands were very new. We pulled near to the 44-acre Yellow Bar, our captain careful to avoid the shallows. Its yellow fields of marsh grasses looked suspiciously monotonous compared to the scrubby, tree-spotted patches of the mainland. That’s because Yellow Bar was completed in April – a five-month-old island from the bottom of the Ambrose Channel. Alongside it were other islands bolstered by Ambrose sand: Elders Point, Black Wall, Stony Creek.

Yellow Bar, completed in April, lies ahead of the boat.

That’s what they were able to do, Baron said, with an annual load of sand of about 3.6 million cubic yards. Unfortunately for Gateway, when the Harbor Deepening Project wraps up in 2014, the Ambrose Channel’s yield will shrink to just 423,000 cubic yards per year.

Next the dredgers will turn to areas near Staten Island, where the channels are cut into the bedrock and must be dredged with explosives. The Army Corps will have to find something else to do with those rocks.